1. Field of the Invention
The present invention relates generally to a method and apparatus for measuring the angle of a slope in relation to a horizontal or vertical plane in applications such as road graders, high extending dump trucks, asphalt paving machines, and drill rigs, among others.
2. Description of the Related Art
Many different operations include machinery which creates a slope or grade having a predetermined angle relative to the horizontal plane. Other types of machinery are used to dig holes that must be as perpendicular as possible relative to the earth's horizontal plane (i.e., vertical). Examples of the above types of machinery are road graders, asphalt paving machines and machinery used in construction and certain drill rig applications, among others.
For example, new roads being built by contractors require a series of grading and surveying operations to develop a roadway with the proper slope. In developing new roadways, a machine referred to as a road grader is used to place a grade of predetermined slope on the sides of the roadway. Road graders are basically constructed in the following manner. The motor, front wheels and rear drive wheels are mounted on a frame with the movable blade mounted between the front and rear wheels. This same frame also holds the seat and cab floor on which the operator either sits or stands.
Two alternative methods are currently available to aid the operator in properly positioning the road grader blade to create the desired percent of cross slope or grade. In the first method, referred to as blue-topping, the operator uses a series of reference points set in the ground that relate to the vertical distance versus the horizontal plane. These points are placed by a survey crew, which is a costly expense. The grader operator must constantly adjust the blade to maintain contact with the ground at the elevation designated by the reference points on either side of the blade. This requires constant attention of the operator to the ground level and the controls, creating a safety hazard. Also, the low road grader speed required to perform this operation greatly reduces productivity.
In the second method, a laser beam sending unit produces a beam which contacts a receiving unit mounted on the grader which indicates the adjustments that must be executed by the grader operator. However, this is only effective in isolated areas due to the separation required between the sending unit and receiving unit. Also, the sending unit must be moved when the grade changes or when the laser beam reaches its limit, which makes this method impractical for many applications.
Because of problems in applying these alternative methods, in many cases the slope graded into the roadway is simply determined by the sense of feel of the operator. Older, full time operators improve this sense of feel after many years of experience. However, most graders are owned by counties or townships and are used part time by operators who do not get enough grader time to develop a sense of feel. Therefore, most rural or country roads develop a negative or excessive slope which makes for poor drainage or erosion. With respect to gravel roads, much gravel is lost every year by improper grading, and in most instances, gravel is lost from the roadway where it cannot be reclaimed. In summary, creating a grade in a roadway using only the operator's sense of feel is commonly done, but it is very inefficient and inexact and many times leads to poor results.
Currently, however, there is no simple and reliable method for aiding an operator in properly forming a grade or slope. Thus, there has been a long-felt need for a simple and reliable method and apparatus which measures the slope of a grade and provides feedback to an operator to assure predictably accurate grades even by relatively inexperienced operators.
In many other applications, it would also be desirable to have an apparatus which provides a reliable determination of slope angle or level. In certain drilling rig or construction applications, for example, it is necessary for the rig to drill a hole that is as perpendicular as possible to the earth's horizontal plane, (i.e., the hole should be vertical). For example, when holes are being dug for piers or other support structures, it is important that the hole be as vertical as possible for maximum strength and support. However, there is currently no method for monitoring the extent to which a hole being dug is perpendicular relative to the earth's local gravity vector.
Considering anther example, certain dump trucks are referred to as high extending dump trucks. If the bed of such a dump truck is raised upward too far, the truck is liable to tip over. Each year in the United States, there are numerous instances of dump trucks tipping over because of the truck bed being extended upward too far or because of load shifting during loading or transport. In such instances, there is much time and expense associated with "righting" the dump trucks. Currently there is no method for monitoring the slope of a dump truck bed and warning the driver or operator when the bed has been extended past safe limits.
In other applications as well, it would be desirable to have a simple device which can accurately measure the slope of a grade and provide this information to a user in real time. Therefore, an apparatus is desired which provides a reliable measurement of the slope of a grade or a level indication.